Progressive Retinal Atrophy
and the
American Eskimo
Information from American Eskimo Health Concerns Web
Written by: Marla Wills
Ajax* was a gorgeous, intelligent, outgoing, nine-month-old miniature American Eskimo when his great-grandmother, Love, was diagnosed with Progressive Retinal Atrophy. Over the next few months, two of Love's older offspring (including Ajax' grandmother), as well as at least three offspring from two of Love's siblings, were also found to be affected. Most of these dogs were top winning show dogs-champions and grand champions-whose previous eye exams had all been normal. They were also top producing dogs, so the defective gene had been widely perpetuated before their vets had even begun to see that there was a problem.
Sassy was an American Eskimo adopted from the Humane Society. Estimated to be about six years old, she gradually began bumping into obstacles in low-light situations and totally misjudging the car door opening.
Sugar was a gift who had been purchased from a small local breeder. At about age six, she also started running into things when the furniture was rearranged and the lights were dim. Although she could still see well enough to chase the cats, when she fell into the swimming pool one evening, her owners knew there was a serious problem. Both Sassy and Sugar were diagnosed with late-stage PRA, and are expected to be totally blind within six months. But thankfully, both are adjusting well.
Another breeder was recently shocked and devastated when told that Lily, a standard American Eskimo, had mid-stage PRA, in spite of generations of foundation stock that were still testing normal at seven to ten years of age. But when the vet dimmed the lights, moved a chair into Lily's path, and she proceeded to blithely walk right into it, there was no doubt in anyone's mind.
Although American Eskimos are generally a very healthy breed, PRA has been found in every type of AE: standards and miniatures, males and females, show dogs and family pets, those with illustrious pedigrees and those whose pedigrees are unknown. Although PRA is not the only genetic problem found in the American Eskimo, or even the most devastating thing that could happen to a dog, it is a problem that is becoming more "visible." It is also a problem for which a solution may be on the horizon, thanks to ongoing research and the help of dedicated owners and breeders who are seeking to find answers.
What is PRA?
Progressive Retinal Atrophy (PRA), also sometimes called Progressive Retinal Degeneration (PRD), refers to a group of inherited retinal disorders that cause blindness in dogs. PRA is found in most breeds of purebred dogs, as well as in mixed-breed dogs.
PRA is not caused by whelping-box heat lamps, trauma, or poor nutrition. It is genetically inherited and affects both eyes. At least six separate forms of PRA have been identified. PRA differs from breed to breed in the age of onset as well as the rate of progression. The end stages of the diseases, however, are very similar in severity, ranging from serious visual impairment to complete blindness. PRA also corresponds to a group of retinal diseases in humans known as retinitis pigmentosa.
The disease is gradual, and is not painful to the dog. By the time humans begin to notice behavioral changes in their dogs, the degeneration is actually quite advanced. Some owners may not even notice any symptoms until they take the dog out of their own homes. These dogs have memorized their furniture and yard layouts and have learned to use other cues such as scents, sounds, and temperature changes. It is only in unfamiliar environments that the vision loss becomes apparent to an observer.
Although there is no cure for PRA at this time, dogs (especially our smart Eskies) adapt well to their darkening world. Resources are also available to help owners cope with their dogs' blindness, so don't panic if your dog is diagnosed as PRA affected. A good resource is "Living with Blind Dogs: A Resource Book and Training Guide for the Owners of Blind & Low Vision Dogs" by Caroline Levin.
The two general types of PRA are early-onset and late-onset. In the early-onset disorders, the visual cells in a puppy's retinas fail to develop normally. Late-onset disease is characterized by the degeneration of the rods and cones in the retina after they have completed normal development. Late-onset PRA is sometimes visible by eye exam in dogs one year old or even younger. In other cases, even early stages of the disease may not be visible to an experienced ophthalmologist until the dog is five or six.
The most widespread and troublesome form of PRA is progressive rod-cone degeneration. Scientists at the James A. Baker Institute for Animal Health at Cornell University, have proven that five breeds of dogs-poodles, American and English cocker spaniels, Labrador retrievers, and Portuguese water dogs-inherit this late-onset form of PRA. Many other breeds are subject to late-onset PRA, and most, if not all, are believed to inherit the prcd defect, including American Eskimos.
Rods are specialized photoreceptor cells in the retina that function primarily in dim light and are responsible for night vision. As PRA progresses, they become shorter and their arrangement becomes increasingly disorganized, causing night blindness to develop. Cone cells allow a dog to see in daylight and are responsible for color perception and overall visual acuity. In time, they suffer the same fate, and the dog loses the ability to see at all. Regardless of the type of PRA, the changes in the rods are more rapid and extensive than the changes in the cones. PRA also causes a gradual reduction in the number and caliber of the blood vessels that nourish the retina. This is a distinct hallmark of the disease, and can be seen when the dog's eyes are dilated and examined through an ophthalmoscope.
How is PRA Inherited?
PRA is believed to be inherited as an autosomal-recessive trait in all breeds except in Siberian huskies. Autosomal means that the trait is not on a sex chromosome, and in order to be affected by a recessive gene, both males and females must inherit a copy of the abnormal, defective gene from each parent. A dog that inherits two normal copies of the gene is said to be genetically clear or normal; a dog that inherits one normal gene and one defective gene is said to be a carrier. Both clear dogs and carriers will function normally, and both will receive "normal" ratings on their Canine Eye Registration Foundation (CERF) exams.
The odds of inheriting a gene for PRA vary according to the genetic status of the parents.
If a dog is affected, BOTH parents must be either carriers or affected.
ALL offspring of PRA affected dogs are either carriers or affected, depending on the gene they received from the other parent.
When two carriers are bred together, they can produce offspring that are affected (25%), carrier (50%), and clear (25%) in the same litter.
A dog that has PRA affected siblings but is still testing normal, has parents that test normal, and is old enough for the results of the test to be significant (4,6,10?) has a 67% chance of being a carrier, and a 33% chance of being clear.
From Breakthroughs in Sight: Progress in PRA Research, 1999, James A. Baker Institute, Cornell University: "The only way to reverse the spread of PRA is to develop the means to identify both affected dogs and carriers, with absolute accuracy, before they are old enough to be sold as pets or breeding stock."
"Unless the chromosomal location of the abnormality is known, the only way to identify a carrier is by tracing back through a pedigree after a dog has been determined to be affected. By the time an affected dog turns up in a family, there are probably already many carriers in the pedigree."
What is Being Done?
The American Eskimo is part of two genetic studies that are currently underway: one at the James A. Baker Institute for Animal Health at Cornell University, and the other at the Veterinary Genetics Lab at University of California-Davis.
The primary goal of PRA research at the Baker Institute has been to identify and locate the exact genetic abnormality that causes each form of the disease. They have developed tests for several breeds of dogs, and are currently studying the American Eskimo. You can read more about the Baker Institute by looking on the internet at http://bakerinstitute.vet.cornell.edu/.
Currently there are two main categories of American Eskimos that are of particular interest to Cornell: (1) dogs that have been diagnosed as PRA affected and (2) dogs that are over the age of 10 and are still testing "normal." Cornell has also requested blood samples, three-generation pedigrees, and eye exam reports from specific dogs in these two categories, as well as dogs that are parents, offspring, or siblings of PRA affected dogs.
UC Davis is working with the canine genetic map that is being developed by an international collaboration. They are creating screening panels that will allow genetic researchers to search for a specific gene by evaluating multiple markers at one time instead of individually. They are also building a comprehensive DNA database by collecting samples which will be tested against those screening panels. This will allow them to establish a genetic profile of each breed and further the understanding of dog genetics. This type of data will also assist in the discovery of genes associated with specific traits and diseases.
The American Eskimo is one of the breeds included in this study and UC Davis is looking for participation from all American Eskimos. There is a simple, painless, procedure where you take a swab from the inside of the dog's cheek, and then send it back to Davis. They have also requested that we include a pedigree and health information on each dog, which will allow them to look for the markers that correlate with genetic diseases such as PRA, epilepsy, and cataracts. They need as many unrelated dogs as possible, and are also interested in PRA affected dogs and their close relatives. All information is kept strictly confidential.
In order to participate, UC Davis will send you a Canine Research Kit, free of charge. You can find out more about this study and request a kit by looking on the internet at http://www.vgl.ucdavis.edu/ or by contacting UC Davis directly at Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, CA 95616-8744, (530) 752-2211, (530) 752-3556 fax.
What Can You do?
The first thing that must be done-the foundation upon which everything else is based-is for as many American Eskimos as possible to be tested annually by a board-certified ophthalmologist. This includes both show and pet dogs, altered or intact, breeding or retired. Even dogs that are already blind or have severe cataracts can be tested to see if the blindness is a result of PRA. It is also important that dogs actively being bred receive CERF certificates and become part of CERF's public database.
Next, participate in the ongoing research. All American Eskimos need to participate in the UC Davis study. Request a kit and send them information on each of your dogs.
Cornell wants specific information on specific types of American Eskimos.
|
If your dog is: |
Send Cornell: |
|
Diagnosed by a board-certified ophthalmologist as PRA affected |
- A copy of the dog's eye exam
- A copy of the dog's 3-generation pedigree
- Your phone number
|
|
Over the age of 10 with "normal" eye exam results |
- A copy of the dog's eye exam
- A copy of the dog's 3-generation pedigree
- A sample of the dog's blood
- Your phone number
|
If Cornell wants more information, such as blood samples or information on related dogs, they will contact you directly.
Cornell has also requested that we channel our communications to them through one person, so as not to disrupt their research time any more than necessary. If you have a dog that fits into one of the above categories, please contact eskiepra@mail.com for details on how to collect the blood and send it to Cornell. All information will be kept strictly confidential. You don't even need to specify which category applies to your dog. You can contact eskiepra@mail.com if you have any other questions, including how to participate in one of the studies or where to acquire the book "Living with Blind Dogs."
Most important, share information about your dogs' test results. Be as open and honest as possible with other breeders and those that are buying your dogs. PRA makes itself apparent late in American Eskimos, usually long after breeding age. Breeders need to be able to carefully analyze pedigree information and eye exam results over several generations as they make breeding decisions. Contact eskiepra@mail.com to include your dogs' eye exam results in our voluntary database.
The breeders of yesterday bred to the best of their ability with the resources that were available at the time, and we have a wonderful breed as a result of their efforts. The breeders of tomorrow will be able to take advantage of sophisticated DNA tests for PRA and other inherited diseases. The breeders of today can only base their decisions on available data and technology. Please make a big contribution to the welfare of the American Eskimo dog. Test your dogs, participate in the research, share information, and breed wisely. The future of our breed depends on it. We're all in this together!
*The names of all dogs have been changed, but the examples are real, and typical of PRA in the American Eskimo.
